Although it is generally agreed that transforming growth factor-beta (TGF) plays a central role in sustaining fibrosis in systemic sclerosis (SSc), the triggers of TGF, TGF activation and TGF intracellular signaling are still unknown. The goal of this grant is to understand how TGF signal activation is up-regulated in SSc focusing on the link between innate immunity, inflammation and fibrosis. New emerging evidence points to the importance of innate immunity and interferons (IFNs) in many autoimmune diseases including SSc, and we found that in addition to upregulated TGF gene expression SSc skin and peripheral blood mononuclear cells (PBMC) also show upregulated IFN gene expression. Interestingly more recently we found that polyIC, a toll like receptor 3 (TLR3) ligand, activates human fibroblasts (fb), inducing not only genes known to be regulated by IFNs but also genes that are induced by TGF, suggesting that TGF activation and then fibrosis is regulated by the innate immune response. Thus this application proposes to investigate how innate immune activation regulates inflammation and scarring through cross talk between IFN/and TGF. One of the most exciting of our preliminary results is that polyIC and IFN both induce Smad1 phosphorylation, indicating crossactivation of TGF signaling by IFN/. In addition we unexpectedly discovered that IFN a receptor 2 (IFNAR2) in mice deficient of the IFN receptor 1 (IFNAR1 -/-) activates a non classical IFN/ pathway, and that this pathway may be involved in entirely new biological functions such as controlling the induction of TGF signaling components. In the first aim, proposed experiments will examine the mechanism controlling the physiologic balance between the induction and suppression of the pro-inflammatory program through cross talk between IFN and TGF in fb from wild type (WT) mice, studying Smad1/2/3 expression and phosphorylation, IRF7 and Smad7 gene expression. Then we will investigate the consequences of aberrant IFN signaling that promote novel cross talk between IFN and TGF, and causing the modified equilibrium in TLR activation promoting the profibrotic phenotype in fb from IFNAR1-/- mice. Aim 2 will explore whether impairment of IFN/ signaling might underlie the pro-fibrotic phenotype that characterizes SSc fb, as we observed in IFNAR1 -/- fb. Experiments in this aim will test the effect of IFN and polyIC on TGF signaling components and the functioning of INF/ signaling in SSc compared to normal fb. Finally we will examine the in vivo expression of selected IFN/ and TGF mediators IRF7 and Smad7, in SSc and control skin. Together, these results should significantly extend our understanding of the role of innate immune activation, IFNs and TGF in dermal fibrosis, enlightening a new standpoint of SSc pathogenesis that IFN/ impairment might be the primary cause of uncontrolled TGF activation. In addition the new finding of IFNAR2 function in controlling activation of TGF signaling, add a novel biological response to the complexity of IFN-mediated signaling potentially influencing the clinical use of therapeutics targeting IFNs not only in SSc but also in other diseases.